When the SELECT trial started in 2001, there were high hopes it would prove that taking vitamin E or selenium could help prevent prostate cancer. The newest results from the trial show just the opposite—that taking selenium or vitamin E can actually increase the odds of developing prostate cancer.
By Patrick Skerrett
Bottom line: men shouldn’t take selenium or vitamin E as a way to prevent prostate cancer, or anything else for that matter.
“I counsel all of my patients to absolutely avoid any dietary supplements that contain selenium or vitamin E—including multivitamins,” says prostate cancer expert Dr. Marc Garnick, a clinical professor of medicine at Harvard Medical School, an oncologist at Beth Israel Deaconess Medical Center, and editor in chief of Harvard’s Annual Report on Prostate Diseases.
The case against selenium and vitamin E
Studies done in the 1980s and 1990s suggested that vitamin E and selenium each somehow protected against prostate cancer. The Selenium and Vitamin E Cancer Prevention Trial (SELECT) was started in 2001 to see if that was true. The 36,000 healthy, middle-aged volunteers were divided into four groups. Each man took two pills a day: 400 international units (IU) of vitamin E plus 200 micrograms of selenium; vitamin E plus a placebo; selenium plus a placebo; or two placebos. Neither the men nor their doctors knew who was taking what.
Although SELECT was supposed to last until 2011, it was stopped three years early because neither vitamin E nor selenium were showing any benefit—and there were hazy warning signs they might be doing some harm.
A new report in the Journal of the National Cancer Institute clarifies the picture. A team of researchers from across the U.S. looked specifically at almost 5,000 of the SELECT volunteers who sent in toenail clippings when they joined the trial. Toenail clippings are a great way to measure how much selenium is in a man’s (or woman’s) body. The new study showed that:
- Taking vitamin E alone boosted the risk of developing high-grade prostate cancer, but only in men who started the study with low selenium levels.
- Taking selenium, either alone or in combination with vitamin E, increased the risk of high-grade prostate cancer in men who started the study with high selenium levels, but not in those with low selenium levels.
- Among men who didn’t take either vitamin E or selenium, those who started the study with high selenium levels were no more likely to have developed prostate cancer than men who started it with low selenium levels. (This means the culprit is added selenium from supplements, not selenium from food.)
“The new data are very troubling, and emphasize that supplements can cause real and tangible harm,” says Dr. Garnick. “Any claims of benefits from dietary supplements must be ignored unless large, controlled, and well-conducted investigations confirm such benefits—which I believe will be a very rare occurrence.”
Schmidt is an award-winning freelance science writer based in Portland, Maine. In addition to writing for Harvard Health Publishing, Charlie has written for Science magazine, the Journal of the National Cancer Institute, Environmental Health Perspectives
